Three dimensional (3-D) imaging, or stereoscopy, is a technique used to create the illusion of depth in an image. In many cases, the 3-D effect of an image is created by providing a slightly different image of a scene to each eye of a viewer. The slightly different images may present two perspectives of the same object, where the perspectives differ from each other in a manner similar to the perspectives that the viewer's eyes may naturally experience when directly viewing a three dimensional scene. When the two images are viewed at the same time, the image is perceived as having depth.
Several methods exist to provide a 3-D effect to an image. An anaglyph image may present the two images for each of the viewer's eyes in different colors, such as red and blue-green. To achieve the 3-D effect, the viewer wears glasses with color filter lenses that filter the color(s) so as to present only one of the images for each eye. Thus, the viewer's right eye receives the red image while the viewer's left eye receives the blue-green image. When the left-eye image and the right-eye image are viewed at the same time, the viewer perceives a 3-D effect. In another example, left-eye and right-eye image are superimposed through polarizing filters such that one image is clockwise polarized and the other image is counter-clockwise polarized. The viewer wears glasses with polarized lenses such that each eye receives only one of the images. In a third example, the 3-D images are presented in a time-multiplexed fashion, such as alternating between images meant for the viewer's right eye and the viewer's left eye. The viewer wears glasses that shutter between the viewer's eyes, allowing the right eye to receive the right eye image and the left eye to receive the left eye image.
To transmit 3-D or “stereo” multimedia content (such as 3-D video or film), both left-eye and right-eye images are sent to a display device in a manner that allows the left-eye and right-eye images to be separately presented to the user's left eye and right eye, respectively. Conventional digital interfaces and transmission standards are not designed to support 3-D content that involves transmitting twice as many video frames as non-stereo video. This is a particular problem for high definition video which requires significantly more data for each frame as compared to standard definition video. Techniques have been developed, however, to squeeze a left-eye frame and a right-eye frame into the space of a single video frame allowing a stereo video to be communicated using conventional digital interfaces and transmission standards. For example, one method transmits the images for both eyes of a 3-D image by fitting the images for the right and left eye into a single frame, in a side-by-side arrangement (e.g., dividing the conventional frame into a left half and right half) or over-under arrangement (e.g., dividing the conventional frame into an upper half and a lower half). In another example, anamorphic squeeze techniques are used to squeeze each of the left-eye and the right-eye images into the smaller space for transmission as a single frame. The two images may then be separated, expanded and presented to the viewer in a manner consistent with 3-D techniques by the display device. Another method involves transmitting both images in a checkerboard fashion in a single frame. Thus, the pixels of the images for each eye are interleaved into a single frame on a pixel-level basis. These methods may provide the data for the two images needed for a single 3-D image at the same rate as 2-D images may be transmitted. However, because two images are being presented in a single frame, the resolution of each image is less than if each frame contained a single image. Thus, the images provided in these schemes may not meet the high resolution requirements of high definition video.
High definition video generally refers to multimedia content presented in a display resolution of 720p or higher. A resolution of 720p indicates that each frame of the image presented has a vertical resolution of 720 pixel lines and that each pixel line of the image is refreshed when the image is updated. A high definition television mode specified as 720p typically has an aspect ratio of 16:9 and, therefore, has a horizontal resolution of 1280 pixels, resulting in 921,600 (720×1280) pixels in each frame. Further, high definition video is often transmitted at 60 frames per second, meaning that the entire image is updated 60 times per second in progressive modes. Video with higher resolutions and frame rates may also satisfy the high definition standard.
Since 3-D content is often transmitted by squeezing or interleaving the images for the left and right eye into a single frame, each of the left-eye and right-eye images can use only half of the pixels available in the frame. For example, a 720p frame can be vertically divided but such a division allows only 360 vertical lines for each image. While some methods exist to improve the appearance of the squeezed or combined images, the transmitted images may no longer satisfy the quality expectations of a high definition image. Thus, what is needed, among other things, is a method and system for encoding and transmitting 3-D multimedia content that meets the resolution expectations of high definition video and is at the same time compatible with existing digital interfaces and transmission standards.